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  <div class="section" id="using-python-on-windows">
<span id="using-on-windows"></span><h1>3. Using Python on Windows<a class="headerlink" href="#using-python-on-windows" title="Permalink to this headline">¶</a></h1>
<p>This document aims to give an overview of Windows-specific behaviour you should
know about when using Python on Microsoft Windows.</p>
<div class="section" id="installing-python">
<h2>3.1. Installing Python<a class="headerlink" href="#installing-python" title="Permalink to this headline">¶</a></h2>
<p>Unlike most Unix systems and services, Windows does not require Python natively
and thus does not pre-install a version of Python.  However, the CPython team
has compiled Windows installers (MSI packages) with every <a class="reference external" href="https://www.python.org/download/releases/">release</a> for many years.</p>
<p>With ongoing development of Python, some platforms that used to be supported
earlier are no longer supported (due to the lack of users or developers).
Check <span class="target" id="index-0"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0011"><strong>PEP 11</strong></a> for details on all unsupported platforms.</p>
<ul class="simple">
<li><a class="reference external" href="http://pythonce.sourceforge.net/">Windows CE</a> is still supported.</li>
<li>The <a class="reference external" href="http://cygwin.com/">Cygwin</a> installer offers to install the Python
interpreter as well (cf. <a class="reference external" href="ftp://ftp.uni-erlangen.de/pub/pc/gnuwin32/cygwin/mirrors/cygnus/release/python">Cygwin package source</a>, <a class="reference external" href="http://www.tishler.net/jason/software/python/">Maintainer releases</a>)</li>
</ul>
<p>See <a class="reference external" href="https://www.python.org/download/windows/">Python for Windows</a>
for detailed information about platforms with pre-compiled installers.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference external" href="http://www.richarddooling.com/index.php/2006/03/14/python-on-xp-7-minutes-to-hello-world/">Python on XP</a></dt>
<dd>&#8220;7 Minutes to &#8220;Hello World!&#8221;&#8221;
by Richard Dooling, 2006</dd>
<dt><a class="reference external" href="http://www.diveintopython.net/installing_python/windows.html">Installing on Windows</a></dt>
<dd>in &#8220;<a class="reference external" href="http://www.diveintopython.net/">Dive into Python: Python from novice to pro</a>&#8221;
by Mark Pilgrim, 2004,
ISBN 1-59059-356-1</dd>
<dt><a class="reference external" href="http://www.swaroopch.com/notes/python/#install_windows">For Windows users</a></dt>
<dd>in &#8220;Installing Python&#8221;
in &#8220;<a class="reference external" href="http://www.swaroopch.com/notes/python/">A Byte of Python</a>&#8221;
by Swaroop C H, 2003</dd>
</dl>
</div>
</div>
<div class="section" id="alternative-bundles">
<h2>3.2. Alternative bundles<a class="headerlink" href="#alternative-bundles" title="Permalink to this headline">¶</a></h2>
<p>Besides the standard CPython distribution, there are modified packages including
additional functionality.  The following is a list of popular versions and their
key features:</p>
<dl class="docutils">
<dt><a class="reference external" href="http://www.activestate.com/activepython/">ActivePython</a></dt>
<dd>Installer with multi-platform compatibility, documentation, PyWin32</dd>
<dt><a class="reference external" href="https://www.enthought.com/products/epd/">Enthought Python Distribution</a></dt>
<dd>Popular modules (such as PyWin32) with their respective documentation, tool
suite for building extensible Python applications</dd>
</dl>
<p>Notice that these packages are likely to install <em>older</em> versions of Python.</p>
</div>
<div class="section" id="configuring-python">
<h2>3.3. Configuring Python<a class="headerlink" href="#configuring-python" title="Permalink to this headline">¶</a></h2>
<p>In order to run Python flawlessly, you might have to change certain environment
settings in Windows.</p>
<div class="section" id="excursus-setting-environment-variables">
<span id="setting-envvars"></span><h3>3.3.1. Excursus: Setting environment variables<a class="headerlink" href="#excursus-setting-environment-variables" title="Permalink to this headline">¶</a></h3>
<p>Windows has a built-in dialog for changing environment variables (following
guide applies to XP classical view): Right-click the icon for your machine
(usually located on your Desktop and called &#8220;My Computer&#8221;) and choose
<em class="menuselection">Properties</em> there.  Then, open the <em class="guilabel">Advanced</em> tab
and click the <em class="guilabel">Environment Variables</em> button.</p>
<p>In short, your path is:</p>
<blockquote>
<div><em class="menuselection">My Computer
‣ Properties
‣ Advanced
‣ Environment Variables</em></div></blockquote>
<p>In this dialog, you can add or modify User and System variables. To change
System variables, you need non-restricted access to your machine
(i.e. Administrator rights).</p>
<p>Another way of adding variables to your environment is using the <strong class="command">set</strong>
command:</p>
<div class="highlight-none"><div class="highlight"><pre>set PYTHONPATH=%PYTHONPATH%;C:\My_python_lib
</pre></div>
</div>
<p>To make this setting permanent, you could add the corresponding command line to
your <tt class="file docutils literal"><span class="pre">autoexec.bat</span></tt>. <strong class="program">msconfig</strong> is a graphical interface to this
file.</p>
<p>Viewing environment variables can also be done more straight-forward: The
command prompt will expand strings wrapped into percent signs automatically:</p>
<div class="highlight-none"><div class="highlight"><pre>echo %PATH%
</pre></div>
</div>
<p>Consult <strong class="command">set /?</strong> for details on this behaviour.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference external" href="http://support.microsoft.com/kb/100843">http://support.microsoft.com/kb/100843</a></dt>
<dd>Environment variables in Windows NT</dd>
<dt><a class="reference external" href="http://support.microsoft.com/kb/310519">http://support.microsoft.com/kb/310519</a></dt>
<dd>How To Manage Environment Variables in Windows XP</dd>
<dt><a class="reference external" href="http://www.chem.gla.ac.uk/~louis/software/faq/q1.html">http://www.chem.gla.ac.uk/~louis/software/faq/q1.html</a></dt>
<dd>Setting Environment variables, Louis J. Farrugia</dd>
</dl>
</div>
</div>
<div class="section" id="finding-the-python-executable">
<span id="windows-path-mod"></span><h3>3.3.2. Finding the Python executable<a class="headerlink" href="#finding-the-python-executable" title="Permalink to this headline">¶</a></h3>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3.</span></p>
</div>
<p>Besides using the automatically created start menu entry for the Python
interpreter, you might want to start Python in the command prompt. As of
Python 3.3, the installer has an option to set that up for you.</p>
<p>At the &#8220;Customize Python 3.3&#8221; screen, an option called
&#8220;Add python.exe to search path&#8221; can be enabled to have the installer place
your installation into the <span class="target" id="index-1"></span><tt class="xref std std-envvar docutils literal"><span class="pre">%PATH%</span></tt>. This allows you to type
<strong class="command">python</strong> to run the interpreter. Thus, you can also execute your
scripts with command line options, see <a class="reference internal" href="cmdline.html#using-on-cmdline"><em>Command line</em></a> documentation.</p>
<p>If you don&#8217;t enable this option at install time, you can always re-run the
installer to choose it.</p>
<p>The alternative is manually modifying the <span class="target" id="index-2"></span><tt class="xref std std-envvar docutils literal"><span class="pre">%PATH%</span></tt> using the
directions in <a class="reference internal" href="#setting-envvars"><em>Excursus: Setting environment variables</em></a>. You need to set your <span class="target" id="index-3"></span><tt class="xref std std-envvar docutils literal"><span class="pre">%PATH%</span></tt>
environment variable to include the directory of your Python distribution,
delimited by a semicolon from other entries. An example variable could look
like this (assuming the first two entries are Windows&#8217; default):</p>
<div class="highlight-none"><div class="highlight"><pre>C:\WINDOWS\system32;C:\WINDOWS;C:\Python33
</pre></div>
</div>
</div>
<div class="section" id="finding-modules">
<h3>3.3.3. Finding modules<a class="headerlink" href="#finding-modules" title="Permalink to this headline">¶</a></h3>
<p>Python usually stores its library (and thereby your site-packages folder) in the
installation directory.  So, if you had installed Python to
<tt class="file docutils literal"><span class="pre">C:\Python\</span></tt>, the default library would reside in
<tt class="file docutils literal"><span class="pre">C:\Python\Lib\</span></tt> and third-party modules should be stored in
<tt class="file docutils literal"><span class="pre">C:\Python\Lib\site-packages\</span></tt>.</p>
<p>This is how <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a> is populated on Windows:</p>
<ul class="simple">
<li>An empty entry is added at the start, which corresponds to the current
directory.</li>
<li>If the environment variable <span class="target" id="index-4"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONPATH"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONPATH</span></tt></a> exists, as described in
<a class="reference internal" href="cmdline.html#using-on-envvars"><em>Environment variables</em></a>, its entries are added next.  Note that on Windows,
paths in this variable must be separated by semicolons, to distinguish them
from the colon used in drive identifiers (<tt class="docutils literal"><span class="pre">C:\</span></tt> etc.).</li>
<li>Additional &#8220;application paths&#8221; can be added in the registry as subkeys of
<tt class="samp docutils literal"><span class="pre">\SOFTWARE\Python\PythonCore\</span><em><span class="pre">version</span></em><span class="pre">\PythonPath</span></tt> under both the
<tt class="docutils literal"><span class="pre">HKEY_CURRENT_USER</span></tt> and <tt class="docutils literal"><span class="pre">HKEY_LOCAL_MACHINE</span></tt> hives.  Subkeys which have
semicolon-delimited path strings as their default value will cause each path
to be added to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>.  (Note that all known installers only use
HKLM, so HKCU is typically empty.)</li>
<li>If the environment variable <span class="target" id="index-5"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONHOME"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONHOME</span></tt></a> is set, it is assumed as
&#8220;Python Home&#8221;.  Otherwise, the path of the main Python executable is used to
locate a &#8220;landmark file&#8221; (<tt class="docutils literal"><span class="pre">Lib\os.py</span></tt>) to deduce the &#8220;Python Home&#8221;.  If a
Python home is found, the relevant sub-directories added to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>
(<tt class="docutils literal"><span class="pre">Lib</span></tt>, <tt class="docutils literal"><span class="pre">plat-win</span></tt>, etc) are based on that folder.  Otherwise, the core
Python path is constructed from the PythonPath stored in the registry.</li>
<li>If the Python Home cannot be located, no <span class="target" id="index-6"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONPATH"><tt class="xref std std-envvar docutils literal"><span class="pre">PYTHONPATH</span></tt></a> is specified in
the environment, and no registry entries can be found, a default path with
relative entries is used (e.g. <tt class="docutils literal"><span class="pre">.\Lib;.\plat-win</span></tt>, etc).</li>
</ul>
<p>The end result of all this is:</p>
<ul class="simple">
<li>When running <tt class="file docutils literal"><span class="pre">python.exe</span></tt>, or any other .exe in the main Python
directory (either an installed version, or directly from the PCbuild
directory), the core path is deduced, and the core paths in the registry are
ignored.  Other &#8220;application paths&#8221; in the registry are always read.</li>
<li>When Python is hosted in another .exe (different directory, embedded via COM,
etc), the &#8220;Python Home&#8221; will not be deduced, so the core path from the
registry is used.  Other &#8220;application paths&#8221; in the registry are always read.</li>
<li>If Python can&#8217;t find its home and there is no registry (eg, frozen .exe, some
very strange installation setup) you get a path with some default, but
relative, paths.</li>
</ul>
</div>
<div class="section" id="executing-scripts">
<h3>3.3.4. Executing scripts<a class="headerlink" href="#executing-scripts" title="Permalink to this headline">¶</a></h3>
<p>As of Python 3.3, Python includes a launcher which facilitates running Python
scripts. See <a class="reference internal" href="#launcher"><em>Python Launcher for Windows</em></a> for more information.</p>
</div>
<div class="section" id="executing-scripts-without-the-python-launcher">
<h3>3.3.5. Executing scripts without the Python launcher<a class="headerlink" href="#executing-scripts-without-the-python-launcher" title="Permalink to this headline">¶</a></h3>
<p>Without the Python launcher installed, Python scripts (files with the extension
<tt class="docutils literal"><span class="pre">.py</span></tt>) will be executed by <strong class="program">python.exe</strong> by default.  This executable
opens a terminal, which stays open even if the program uses a GUI.  If you do
not want this to happen, use the extension <tt class="docutils literal"><span class="pre">.pyw</span></tt> which will cause the script
to be executed by <strong class="program">pythonw.exe</strong> by default (both executables are
located in the top-level of your Python installation directory).  This
suppresses the terminal window on startup.</p>
<p>You can also make all <tt class="docutils literal"><span class="pre">.py</span></tt> scripts execute with <strong class="program">pythonw.exe</strong>,
setting this through the usual facilities, for example (might require
administrative rights):</p>
<ol class="arabic">
<li><p class="first">Launch a command prompt.</p>
</li>
<li><p class="first">Associate the correct file group with <tt class="docutils literal"><span class="pre">.py</span></tt> scripts:</p>
<div class="highlight-none"><div class="highlight"><pre>assoc .py=Python.File
</pre></div>
</div>
</li>
<li><p class="first">Redirect all Python files to the new executable:</p>
<div class="highlight-none"><div class="highlight"><pre>ftype Python.File=C:\Path\to\pythonw.exe &quot;%1&quot; %*
</pre></div>
</div>
</li>
</ol>
</div>
</div>
<div class="section" id="python-launcher-for-windows">
<span id="launcher"></span><h2>3.4. Python Launcher for Windows<a class="headerlink" href="#python-launcher-for-windows" title="Permalink to this headline">¶</a></h2>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.3.</span></p>
</div>
<p>The Python launcher for Windows is a utility which aids in the location and
execution of different Python versions.  It allows scripts (or the
command-line) to indicate a preference for a specific Python version, and
will locate and execute that version.</p>
<div class="section" id="getting-started">
<h3>3.4.1. Getting started<a class="headerlink" href="#getting-started" title="Permalink to this headline">¶</a></h3>
<div class="section" id="from-the-command-line">
<h4>3.4.1.1. From the command-line<a class="headerlink" href="#from-the-command-line" title="Permalink to this headline">¶</a></h4>
<p>You should ensure the launcher is on your PATH - depending on how it was
installed it may already be there, but check just in case it is not.</p>
<p>From a command-prompt, execute the following command:</p>
<div class="highlight-none"><div class="highlight"><pre>py
</pre></div>
</div>
<p>You should find that the latest version of Python 2.x you have installed is
started - it can be exited as normal, and any additional command-line
arguments specified will be sent directly to Python.</p>
<p>If you have multiple versions of Python 2.x installed (e.g., 2.6 and 2.7) you
will have noticed that Python 2.7 was started - to launch Python 2.6, try the
command:</p>
<div class="highlight-none"><div class="highlight"><pre>py -2.6
</pre></div>
</div>
<p>If you have a Python 3.x installed, try the command:</p>
<div class="highlight-none"><div class="highlight"><pre>py -3
</pre></div>
</div>
<p>You should find the latest version of Python 3.x starts.</p>
</div>
<div class="section" id="from-a-script">
<h4>3.4.1.2. From a script<a class="headerlink" href="#from-a-script" title="Permalink to this headline">¶</a></h4>
<p>Let&#8217;s create a test Python script - create a file called <tt class="docutils literal"><span class="pre">hello.py</span></tt> with the
following contents</p>
<div class="highlight-none"><div class="highlight"><pre>#! python
import sys
sys.stdout.write(&quot;hello from Python %s\n&quot; % (sys.version,))
</pre></div>
</div>
<p>From the directory in which hello.py lives, execute the command:</p>
<div class="highlight-none"><div class="highlight"><pre>py hello.py
</pre></div>
</div>
<p>You should notice the version number of your latest Python 2.x installation
is printed.  Now try changing the first line to be:</p>
<div class="highlight-none"><div class="highlight"><pre>#! python3
</pre></div>
</div>
<p>Re-executing the command should now print the latest Python 3.x information.
As with the above command-line examples, you can specify a more explicit
version qualifier.  Assuming you have Python 2.6 installed, try changing the
first line to <tt class="docutils literal"><span class="pre">#!</span> <span class="pre">python2.6</span></tt> and you should find the 2.6 version
information printed.</p>
</div>
<div class="section" id="from-file-associations">
<h4>3.4.1.3. From file associations<a class="headerlink" href="#from-file-associations" title="Permalink to this headline">¶</a></h4>
<p>The launcher should have been associated with Python files (i.e. <tt class="docutils literal"><span class="pre">.py</span></tt>,
<tt class="docutils literal"><span class="pre">.pyw</span></tt>, <tt class="docutils literal"><span class="pre">.pyc</span></tt>, <tt class="docutils literal"><span class="pre">.pyo</span></tt> files) when it was installed.  This means that
when you double-click on one of these files from Windows explorer the launcher
will be used, and therefore you can use the same facilities described above to
have the script specify the version which should be used.</p>
<p>The key benefit of this is that a single launcher can support multiple Python
versions at the same time depending on the contents of the first line.</p>
</div>
</div>
<div class="section" id="shebang-lines">
<h3>3.4.2. Shebang Lines<a class="headerlink" href="#shebang-lines" title="Permalink to this headline">¶</a></h3>
<p>If the first line of a script file starts with <tt class="docutils literal"><span class="pre">#!</span></tt>, it is known as a
&#8220;shebang&#8221; line.  Linux and other Unix like operating systems have native
support for such lines and are commonly used on such systems to indicate how
a script should be executed.  This launcher allows the same facilities to be
using with Python scripts on Windows and the examples above demonstrate their
use.</p>
<p>To allow shebang lines in Python scripts to be portable between Unix and
Windows, this launcher supports a number of &#8216;virtual&#8217; commands to specify
which interpreter to use.  The supported virtual commands are:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">/usr/bin/env</span> <span class="pre">python</span></tt></li>
<li><tt class="docutils literal"><span class="pre">/usr/bin/python</span></tt></li>
<li><tt class="docutils literal"><span class="pre">/usr/local/bin/python</span></tt></li>
<li><tt class="docutils literal"><span class="pre">python</span></tt></li>
</ul>
<p>For example, if the first line of your script starts with</p>
<div class="highlight-none"><div class="highlight"><pre>#! /usr/bin/python
</pre></div>
</div>
<p>The default Python will be located and used.  As many Python scripts written
to work on Unix will already have this line, you should find these scripts can
be used by the launcher without modification.  If you are writing a new script
on Windows which you hope will be useful on Unix, you should use one of the
shebang lines starting with <tt class="docutils literal"><span class="pre">/usr</span></tt>.</p>
</div>
<div class="section" id="arguments-in-shebang-lines">
<h3>3.4.3. Arguments in shebang lines<a class="headerlink" href="#arguments-in-shebang-lines" title="Permalink to this headline">¶</a></h3>
<p>The shebang lines can also specify additional options to be passed to the
Python interpreter.  For example, if you have a shebang line:</p>
<div class="highlight-none"><div class="highlight"><pre>#! /usr/bin/python -v
</pre></div>
</div>
<p>Then Python will be started with the <tt class="docutils literal"><span class="pre">-v</span></tt> option</p>
</div>
<div class="section" id="customization">
<h3>3.4.4. Customization<a class="headerlink" href="#customization" title="Permalink to this headline">¶</a></h3>
<div class="section" id="customization-via-ini-files">
<h4>3.4.4.1. Customization via INI files<a class="headerlink" href="#customization-via-ini-files" title="Permalink to this headline">¶</a></h4>
<blockquote>
<div><p>Two .ini files will be searched by the launcher - <tt class="docutils literal"><span class="pre">py.ini</span></tt> in the
current user&#8217;s &#8220;application data&#8221; directory (i.e. the directory returned
by calling the Windows function SHGetFolderPath with CSIDL_LOCAL_APPDATA)
and <tt class="docutils literal"><span class="pre">py.ini</span></tt> in the same directory as the launcher.  The same .ini
files are used for both the &#8216;console&#8217; version of the launcher (i.e.
py.exe) and for the &#8216;windows&#8217; version (i.e. pyw.exe)</p>
<p>Customization specified in the &#8220;application directory&#8221; will have
precedence over the one next to the executable, so a user, who may not
have write access to the .ini file next to the launcher, can override
commands in that global .ini file)</p>
</div></blockquote>
</div>
<div class="section" id="customizing-default-python-versions">
<h4>3.4.4.2. Customizing default Python versions<a class="headerlink" href="#customizing-default-python-versions" title="Permalink to this headline">¶</a></h4>
<p>In some cases, a version qualifier can be included in a command to dictate
which version of Python will be used by the command. A version qualifier
starts with a major version number and can optionally be followed by a period
(&#8216;.&#8217;) and a minor version specifier. If the minor qualifier is specified, it
may optionally be followed by &#8220;-32&#8221; to indicate the 32-bit implementation of
that version be used.</p>
<p>For example, a shebang line of <tt class="docutils literal"><span class="pre">#!python</span></tt> has no version qualifier, while
<tt class="docutils literal"><span class="pre">#!python3</span></tt> has a version qualifier which specifies only a major version.</p>
<p>If no version qualifiers are found in a command, the environment variable
<tt class="docutils literal"><span class="pre">PY_PYTHON</span></tt> can be set to specify the default version qualifier - the default
value is &#8220;2&#8221;. Note this value could specify just a major version (e.g. &#8220;2&#8221;) or
a major.minor qualifier (e.g. &#8220;2.6&#8221;), or even major.minor-32.</p>
<p>If no minor version qualifiers are found, the environment variable
<tt class="docutils literal"><span class="pre">PY_PYTHON{major}</span></tt> (where <tt class="docutils literal"><span class="pre">{major}</span></tt> is the current major version qualifier
as determined above) can be set to specify the full version. If no such option
is found, the launcher will enumerate the installed Python versions and use
the latest minor release found for the major version, which is likely,
although not guaranteed, to be the most recently installed version in that
family.</p>
<p>On 64-bit Windows with both 32-bit and 64-bit implementations of the same
(major.minor) Python version installed, the 64-bit version will always be
preferred. This will be true for both 32-bit and 64-bit implementations of the
launcher - a 32-bit launcher will prefer to execute a 64-bit Python installation
of the specified version if available. This is so the behavior of the launcher
can be predicted knowing only what versions are installed on the PC and
without regard to the order in which they were installed (i.e., without knowing
whether a 32 or 64-bit version of Python and corresponding launcher was
installed last). As noted above, an optional &#8220;-32&#8221; suffix can be used on a
version specifier to change this behaviour.</p>
<p>Examples:</p>
<ul class="simple">
<li>If no relevant options are set, the commands <tt class="docutils literal"><span class="pre">python</span></tt> and
<tt class="docutils literal"><span class="pre">python2</span></tt> will use the latest Python 2.x version installed and
the command <tt class="docutils literal"><span class="pre">python3</span></tt> will use the latest Python 3.x installed.</li>
<li>The commands <tt class="docutils literal"><span class="pre">python3.1</span></tt> and <tt class="docutils literal"><span class="pre">python2.7</span></tt> will not consult any
options at all as the versions are fully specified.</li>
<li>If <tt class="docutils literal"><span class="pre">PY_PYTHON=3</span></tt>, the commands <tt class="docutils literal"><span class="pre">python</span></tt> and <tt class="docutils literal"><span class="pre">python3</span></tt> will both use
the latest installed Python 3 version.</li>
<li>If <tt class="docutils literal"><span class="pre">PY_PYTHON=3.1-32</span></tt>, the command <tt class="docutils literal"><span class="pre">python</span></tt> will use the 32-bit
implementation of 3.1 whereas the command <tt class="docutils literal"><span class="pre">python3</span></tt> will use the latest
installed Python (PY_PYTHON was not considered at all as a major
version was specified.)</li>
<li>If <tt class="docutils literal"><span class="pre">PY_PYTHON=3</span></tt> and <tt class="docutils literal"><span class="pre">PY_PYTHON3=3.1</span></tt>, the commands
<tt class="docutils literal"><span class="pre">python</span></tt> and <tt class="docutils literal"><span class="pre">python3</span></tt> will both use specifically 3.1</li>
</ul>
<p>In addition to environment variables, the same settings can be configured
in the .INI file used by the launcher.  The section in the INI file is
called <tt class="docutils literal"><span class="pre">[defaults]</span></tt> and the key name will be the same as the
environment variables without the leading <tt class="docutils literal"><span class="pre">PY_</span></tt> prefix (and note that
the key names in the INI file are case insensitive.)  The contents of
an environment variable will override things specified in the INI file.</p>
<p>For example:</p>
<ul class="simple">
<li>Setting <tt class="docutils literal"><span class="pre">PY_PYTHON=3.1</span></tt> is equivalent to the INI file containing:</li>
</ul>
<div class="highlight-none"><div class="highlight"><pre>[defaults]
python=3.1
</pre></div>
</div>
<ul class="simple">
<li>Setting <tt class="docutils literal"><span class="pre">PY_PYTHON=3</span></tt> and <tt class="docutils literal"><span class="pre">PY_PYTHON3=3.1</span></tt> is equivalent to the INI file
containing:</li>
</ul>
<div class="highlight-none"><div class="highlight"><pre>[defaults]
python=3
python3=3.1
</pre></div>
</div>
</div>
</div>
<div class="section" id="diagnostics">
<h3>3.4.5. Diagnostics<a class="headerlink" href="#diagnostics" title="Permalink to this headline">¶</a></h3>
<p>If an environment variable <tt class="docutils literal"><span class="pre">PYLAUNCH_DEBUG</span></tt> is set (to any value), the
launcher will print diagnostic information to stderr (i.e. to the console).
While this information manages to be simultaneously verbose <em>and</em> terse, it
should allow you to see what versions of Python were located, why a
particular version was chosen and the exact command-line used to execute the
target Python.</p>
</div>
</div>
<div class="section" id="additional-modules">
<h2>3.5. Additional modules<a class="headerlink" href="#additional-modules" title="Permalink to this headline">¶</a></h2>
<p>Even though Python aims to be portable among all platforms, there are features
that are unique to Windows.  A couple of modules, both in the standard library
and external, and snippets exist to use these features.</p>
<p>The Windows-specific standard modules are documented in
<a class="reference internal" href="../library/windows.html#mswin-specific-services"><em>MS Windows Specific Services</em></a>.</p>
<div class="section" id="pywin32">
<h3>3.5.1. PyWin32<a class="headerlink" href="#pywin32" title="Permalink to this headline">¶</a></h3>
<p>The <a class="reference external" href="http://python.net/crew/mhammond/win32/">PyWin32</a> module by Mark Hammond
is a collection of modules for advanced Windows-specific support.  This includes
utilities for:</p>
<ul class="simple">
<li><a class="reference external" href="http://www.microsoft.com/com/">Component Object Model</a> (COM)</li>
<li>Win32 API calls</li>
<li>Registry</li>
<li>Event log</li>
<li><a class="reference external" href="http://msdn.microsoft.com/en-us/library/fe1cf721%28VS.80%29.aspx">Microsoft Foundation Classes</a> (MFC)
user interfaces</li>
</ul>
<p><a class="reference external" href="http://web.archive.org/web/20060524042422/https://www.python.org/windows/pythonwin/">PythonWin</a> is a sample MFC application
shipped with PyWin32.  It is an embeddable IDE with a built-in debugger.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference external" href="http://timgolden.me.uk/python/win32_how_do_i.html">Win32 How Do I...?</a></dt>
<dd>by Tim Golden</dd>
<dt><a class="reference external" href="http://www.boddie.org.uk/python/COM.html">Python and COM</a></dt>
<dd>by David and Paul Boddie</dd>
</dl>
</div>
</div>
<div class="section" id="cx-freeze">
<h3>3.5.2. cx_Freeze<a class="headerlink" href="#cx-freeze" title="Permalink to this headline">¶</a></h3>
<p><a class="reference external" href="http://cx-freeze.sourceforge.net/">cx_Freeze</a> is a <a class="reference internal" href="../library/distutils.html#module-distutils" title="distutils: Support for building and installing Python modules into an existing Python installation."><tt class="xref py py-mod docutils literal"><span class="pre">distutils</span></tt></a>
extension (see <a class="reference internal" href="../distutils/extending.html#extending-distutils"><em>Extending Distutils</em></a>) which wraps Python scripts into
executable Windows programs (<tt class="file docutils literal"><em><span class="pre">*</span></em><span class="pre">.exe</span></tt> files).  When you have done this,
you can distribute your application without requiring your users to install
Python.</p>
</div>
<div class="section" id="wconio">
<h3>3.5.3. WConio<a class="headerlink" href="#wconio" title="Permalink to this headline">¶</a></h3>
<p>Since Python&#8217;s advanced terminal handling layer, <a class="reference internal" href="../library/curses.html#module-curses" title="curses: An interface to the curses library, providing portable terminal handling. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">curses</span></tt></a>, is restricted to
Unix-like systems, there is a library exclusive to Windows as well: Windows
Console I/O for Python.</p>
<p><a class="reference external" href="http://newcenturycomputers.net/projects/wconio.html">WConio</a> is a wrapper for
Turbo-C&#8217;s <tt class="file docutils literal"><span class="pre">CONIO.H</span></tt>, used to create text user interfaces.</p>
</div>
</div>
<div class="section" id="compiling-python-on-windows">
<h2>3.6. Compiling Python on Windows<a class="headerlink" href="#compiling-python-on-windows" title="Permalink to this headline">¶</a></h2>
<p>If you want to compile CPython yourself, first thing you should do is get the
<a class="reference external" href="https://www.python.org/download/source/">source</a>. You can download either the
latest release&#8217;s source or just grab a fresh <a class="reference external" href="https://docs.python.org/devguide/setup.html#getting-the-source-code">checkout</a>.</p>
<p>The source tree contains a build solution and project files for Microsoft
Visual C++, which is the compiler used to build the official Python releases.
View the <tt class="file docutils literal"><span class="pre">readme.txt</span></tt> in their respective directories:</p>
<table border="1" class="docutils">
<colgroup>
<col width="35%" />
<col width="25%" />
<col width="40%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Directory</th>
<th class="head">MSVC version</th>
<th class="head">Visual Studio version</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><tt class="file docutils literal"><span class="pre">PC/VS9.0/</span></tt></td>
<td>9.0</td>
<td>2008</td>
</tr>
<tr class="row-odd"><td><tt class="file docutils literal"><span class="pre">PCbuild/</span></tt></td>
<td>10.0</td>
<td>2010</td>
</tr>
</tbody>
</table>
<p>Note that any build directories within the <tt class="file docutils literal"><span class="pre">PC</span></tt> directory are not
necessarily fully supported.  The <tt class="file docutils literal"><span class="pre">PCbuild</span></tt> directory contains the files
for the compiler used to build the official release.</p>
<p>Check <tt class="file docutils literal"><span class="pre">PCbuild/readme.txt</span></tt> for general information on the build process.</p>
<p>For extension modules, consult <a class="reference internal" href="../extending/windows.html#building-on-windows"><em>Building C and C++ Extensions on Windows</em></a>.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference external" href="http://sebsauvage.net/python/mingw.html">Python + Windows + distutils + SWIG + gcc MinGW</a></dt>
<dd>or &#8220;Creating Python extensions in C/C++ with SWIG and compiling them with
MinGW gcc under Windows&#8221; or &#8220;Installing Python extension with distutils
and without Microsoft Visual C++&#8221; by Sébastien Sauvage, 2003</dd>
<dt><a class="reference external" href="http://oldwiki.mingw.org/index.php/Python%20extensions">MingW &#8211; Python extensions</a></dt>
<dd>by Trent Apted et al, 2007</dd>
</dl>
</div>
</div>
<div class="section" id="other-resources">
<h2>3.7. Other resources<a class="headerlink" href="#other-resources" title="Permalink to this headline">¶</a></h2>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference external" href="http://shop.oreilly.com/product/9781565926219.do">Python Programming On Win32</a></dt>
<dd>&#8220;Help for Windows Programmers&#8221;
by Mark Hammond and Andy Robinson, O&#8217;Reilly Media, 2000,
ISBN 1-56592-621-8</dd>
<dt><a class="reference external" href="http://www.imladris.com/Scripts/PythonForWindows.html">A Python for Windows Tutorial</a></dt>
<dd>by Amanda Birmingham, 2004</dd>
<dt><span class="target" id="index-7"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0397"><strong>PEP 397</strong></a> - Python launcher for Windows</dt>
<dd>The proposal for the launcher to be included in the Python distribution.</dd>
</dl>
</div>
</div>
</div>


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  <h3><a href="../contents.html">Table Of Contents</a></h3>
  <ul>
<li><a class="reference internal" href="#">3. Using Python on Windows</a><ul>
<li><a class="reference internal" href="#installing-python">3.1. Installing Python</a></li>
<li><a class="reference internal" href="#alternative-bundles">3.2. Alternative bundles</a></li>
<li><a class="reference internal" href="#configuring-python">3.3. Configuring Python</a><ul>
<li><a class="reference internal" href="#excursus-setting-environment-variables">3.3.1. Excursus: Setting environment variables</a></li>
<li><a class="reference internal" href="#finding-the-python-executable">3.3.2. Finding the Python executable</a></li>
<li><a class="reference internal" href="#finding-modules">3.3.3. Finding modules</a></li>
<li><a class="reference internal" href="#executing-scripts">3.3.4. Executing scripts</a></li>
<li><a class="reference internal" href="#executing-scripts-without-the-python-launcher">3.3.5. Executing scripts without the Python launcher</a></li>
</ul>
</li>
<li><a class="reference internal" href="#python-launcher-for-windows">3.4. Python Launcher for Windows</a><ul>
<li><a class="reference internal" href="#getting-started">3.4.1. Getting started</a><ul>
<li><a class="reference internal" href="#from-the-command-line">3.4.1.1. From the command-line</a></li>
<li><a class="reference internal" href="#from-a-script">3.4.1.2. From a script</a></li>
<li><a class="reference internal" href="#from-file-associations">3.4.1.3. From file associations</a></li>
</ul>
</li>
<li><a class="reference internal" href="#shebang-lines">3.4.2. Shebang Lines</a></li>
<li><a class="reference internal" href="#arguments-in-shebang-lines">3.4.3. Arguments in shebang lines</a></li>
<li><a class="reference internal" href="#customization">3.4.4. Customization</a><ul>
<li><a class="reference internal" href="#customization-via-ini-files">3.4.4.1. Customization via INI files</a></li>
<li><a class="reference internal" href="#customizing-default-python-versions">3.4.4.2. Customizing default Python versions</a></li>
</ul>
</li>
<li><a class="reference internal" href="#diagnostics">3.4.5. Diagnostics</a></li>
</ul>
</li>
<li><a class="reference internal" href="#additional-modules">3.5. Additional modules</a><ul>
<li><a class="reference internal" href="#pywin32">3.5.1. PyWin32</a></li>
<li><a class="reference internal" href="#cx-freeze">3.5.2. cx_Freeze</a></li>
<li><a class="reference internal" href="#wconio">3.5.3. WConio</a></li>
</ul>
</li>
<li><a class="reference internal" href="#compiling-python-on-windows">3.6. Compiling Python on Windows</a></li>
<li><a class="reference internal" href="#other-resources">3.7. Other resources</a></li>
</ul>
</li>
</ul>

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